It's hard to acclimate in the short run. I find if I avoid getting used to air conditioning (i.e., we keep it around 76-78 degrees during the day inside, and turn that down to 74 at night), and I do a fair amount of outside activity (yardwork, etc.) even when it's hot, and on top of that build up bike mileage as the temps gradually increase, then it's easy to handle. Last summer I was riding in 95 degree weather with high humidity and full sun, and riding comfortably -- but only because I'd been riding when it was in the 80s the month before, and so on. This year I've already done some long rides with temps in the mid 80s and blazing sun.

Sun sleeves for the legs, long sleeve sun reflecting jersey, lots of sun screen, electrolyte tabs, plenty of fluids, and just spending lots of time outside. It gets to where I can't stand to be in the typical air conditioned space in the summer. Just build up to it, regularly. Your body can adapt, you can reset your internal thermostat, but it takes discipline.